In the newest Return of Them beta, we have added some changes to our post processing system, the most important of these is the fact that mods can now add custom post processing filters. This is not an explanation of how to actually write post processing shaders, google will be your friend for that, this is just an explanation of how the Lua API links up to the OpenGL Shading Language, or GLSL for short. Inside the spoiler is the list of all the calls defined in the engine and what arg